It has been known for some time that the purification of exhaust gases may be carried out by using catalysts which are deposited on ceramic carrier materials of various sorts. The use of ceramic carriers has the disadvantage, however, that many of them are sensitive to mechanical stresses and must be built into the exhaust system of the vehicle by means of an additional specially designed support or housing device which is separate and distinct from the exhaust pipe itself.
The carrier catalysts and their housings require, as does any thermoreactor, additional space near the engine for their attachment in order for proper functioning. Since frequently there is very little free space under the hood of a car or under the chassis of the vehicle, any arrangement which decreases the space required for the catalyst reactor housing represents an advantage.
Catalysts have also been described in the prior art which employ a metal carrier for the catalytically active substance. Thus, the German No. OS 22 51 631 describes a process for the purification of exhaust gases employing a catalyst deposited on a metallic carrier made of an electrically conductive material.
According to German No. OS 23 51 237 and German No. AS 23 04 351, a catalytically active material is deposited onto a metal carrier, which may be formed into a shape similar to a ceramic monolithic carrier. For these carriers as well as for the metal carrier shown in German No. OS 24 50 664, a large geometric surface is required.
In the German No. OS 23 13 040 the requirement of little loss of pressure as a result of the catalyst is pointed out. The catalyst described therein, however, requires considerable quantities of costly high temperature and corrosion resistantmetal.
In the catalyst according to the German No. OS 24 53 538, the carrier itself is catalytically active, similar to the case of the known Gould catalyst which consists of a nickel/copper alloy, for the reduction of nitrogen oxides. One disadvantage, however, of this type of catalyst and also as described in German No. AS 21 64 123 is the small specific surface, which offers no ideal conditions for the catalytic reaction of the gas molecules on the active metal.
Generally, the catalysts known up to the present time are expensive and require special containers or housings and as a result take up considerable volume and space.